KR20000052997A - Method and apparatus for performing data rate determination - Google Patents

Abstract

PURPOSE: A method and an apparatus for performing rate determination are provided to improve system and determine the transmission rate of communications in a variable rate communications system in order to use a variable rate vocoder for encoding and decoding speech at a plurality of discrete rates. CONSTITUTION: A vocoder at a transmitter encodes a frame of data into symbols according to one of a set of discrete data rates. When the data rate is lower than the maximum, each symbol is repeated a number of times as required to achieve a constant number of symbols in each frame. The data signal is transmitted at a power proportional to the data rate of the frame. A reference signal is also transmitted. The reference signal is transmitted at a constant power. Further, the data signal has the same carrier frequency as a reference signal so that they exhibit the same fading characteristics as they are transmitted through the channel. At a receiver, the power of the data signal and the power of reference signal are measured as received. The ratio of the power of the data signal to the power of the reference signal is compared with a predetermined ratio of the power of a maximum rate data signal to the power of the reference signal. The result of the comparison will indicate the encoded data rate of the received frame of data. The rate determined by the rate determination system is then used to properly decode the frame of data. A vocoder at the receiver further processes the data for interface with the user.

Description

METHOD AND APPARATUS FOR SETTING DATA RATE {METHOD AND APPARATUS FOR PERFORMING DATA RATE DETERMINATION}

Code Division Multiple Processing (CDMA) modulation technology is one of the technologies that facilitate the communication used by a large number of system users. Other techniques are known, such as time division multiple processing (TDMA), frequency division multiple processing (FDMA), and AM modulation, such as amplitude companded single sideband (ACSSB). CDMA has a number of advantages over these other technologies. The use of CDMA technology in a multiple access communication system is assigned to the assignee of the present invention and is disclosed in US Pat.

CDMA systems frequently use variable rate vocoders to encode data such that the data rate can vary from one data frame to another. Exemplary embodiments of variable rate vocoder are disclosed in US Pat. No. 5,414,796, entitled "VARIABLE RATE VOCODER", assigned to the assignee of the present invention and referenced herein. The use of variable rate communication channels reduces mutual interference by eliminating unnecessary transmissions when voice that is not useful is transmitted. An algorithm is used in the vocoder to generate a variable of the information bits of each frame as the voice activity varies. For example, a vocoder with one set of four rates may generate a 20 millisecond data frame containing 16, 40, 80, or 171 information bits, depending on the activity of the speaker. In communication, it is desirable to transmit each data frame at a predetermined time by varying the transmission rate. An additional description of formatting vocoder data into a data frame is disclosed in US Pat. No. 5,511,073, assigned to the assignee of the present invention and referred to herein under the heading "METHOD AND APPARATUS FOR THE FORMATTING OF DATA FOR TRANSMISSION." . The data frame is further processed, spread spectrum modulated, as disclosed under the heading "SYSTEM AND METHOD FOR GENERATING WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM" to U.S. Patent No. 5,103,459, which is assigned to the assignee of the present invention and referenced herein. May be sent.

Variable rate systems can be developed to include specified rate information. If the rate is included as part of a variable rate frame, the frame is properly decoded in advance, and the rate does not recover even after the rate has already been set. Rather than including the rate in a variable rate frame, it is preferable to send the rate to the non-variable rate portion of the frame instead. However, only a few bits are typically required to indicate the rate, and these bits cannot be effectively encoded and interposed to provide error protection for padding the communication channel. Moreover, the rate information is variable only after some decoding delay or error has occurred.

Optionally, a variable rate system can be developed that does not include specified rate information. One technique for the receiver to determine the rate of a received data frame for which rate information is not explicitly included in the frame is US Patent Application No. 08, filed April 26, 1994, assigned to the assignee of the present invention and referenced herein. / 233,570, entitled "METHOD AND APPARATUS FOR DETERMINING DATA RATE OF TRANSMITTED VARIABLE RATE DATA IN A COMMUNICATIONS RECEIVER." Other techniques are disclosed in U.S. Patent Application No. 08 / 126,477, filed September 24, 1993, assigned to the assignee of the present invention and referenced herein under the heading "MULTIRATE SERIAL VITERBI DECODER FOR CODE DIVISION MULTIPLE ACCESS SYSTEM APPLICATIONS." There is. According to these techniques, each received data frame is decoded at each possible rate. An error matrix is provided to the processor indicating the quality of the decoded symbol for each frame decoded at each rate. The error matrix may include the Cyclic Redundancy Check (CRC) result, the Yamamoto quality metrics and the symbol error rate. These error matrices are known in communication systems. The processor analyzes the error matrix and sets the most appropriate rate at which incoming symbols were sent.

Each received data frame is decoded at each possible data rate, resulting in the desired decoded data. However, searching through all possible rates is not the most efficient use of the receiver's resource processing. In addition, since a high transmission rate is used, power consumption increases when setting the transmission rate. This is because there are more bits per frame to be processed. Also, as technology develops, larger sets of data rates for communication information may be used. The use of larger sets of rates makes it impossible to decode all at all possible rates. Decoding delay is not applicable to some systems. As a result, a more efficient rate setting system is required in a variable rate communication environment. These problems and disadvantages are clearly present in the prior art and solved by the present invention according to the following description.

Summary of the Invention

The present invention relates to a novel and improved method and apparatus for setting a communication transmission rate of a variable rate communication system. Although the present invention can be used in many communication systems, it is particularly useful in cellular communication systems that employ a variable rate vocoder that encodes and decodes speech at a plurality of different rates. Such communication systems include mobile telephones, personal communication devices, wireless subscriber lines, and branch exchanges. The present invention is described under the background for a code division multiple processing (CDMA) communication system but is equally applicable to other transmission formats.

The Telecommunications Industry Association (TIA) has provided a standard CDMA communication called "IS-95-A Mobile Station-Base Station Compatibility Standard for Dual Mode Wideband Spread Spectrum Cellular System" (hereinafter referred to as IS-95-A). IS-95-A is used for transmission of variable rate data. The present invention describes the transmission of multiplex option 1 data which transmits data at 9600, 4800, 2400 and 1200 bits / sec at full, half, quarter and 1/8 rates, respectively. Data transmission in IS-95-A compatible systems is provided in 20 millisecond frames. A full rate frame contains twice the number of bits of a half rate frame, a half rate contains twice the number of bits of a quarter rate frame, and a quarter rate frame contains twice the number of bits of an 1/8 rate frame. do. On the IS-95-A forward link, symbol repetition is introduced to occupy the full capacity of the output frame. Each symbol in the half rate frame is provided twice in the output frame, each symbol in the quarter rate frame is provided four times, and each symbol in the eighth rate frame is provided eight times.

Since the receiver can take advantage of redundancy in the frame, frames transmitted below the full rate are transmitted at lower energy than full rate frames. In an exemplary embodiment, the half rate frame is transmitted at half the energy of the full rate frame, the quarter leaf frame is transmitted at one quarter of the full rate prem energy, and the 1/8 rate frame is one third of the full rate frame energy. Is sent as 8

In addition to data frame transmission, transmitters in variable rate communication systems transmit reference signals at carrier frequencies that are approximately equal to the data signals.

At the receiver, each received frame of data is compared with a reference signal. In particular, the ratio of the power of the reference signal to the power of the received data frame is compared with the predetermined ratio of the reference signal power and the power of the data prem encoded at the maximum rate. Based on the relationship between the two ratios, the transmission rate of the received data frame can be set prior to decoding. One way of using the rate setting operation of the present invention is to provide a signal indicative of the transmission rate to the decoder in order to properly and effectively decode the received data frame.

Brief description of the drawings

The features, objects, and advantages of the present invention will become apparent from the following detailed description with reference to the accompanying drawings, in which reference characters are identified.

1 is a schematic diagram of an exemplary CDMA cellular telephone system.

2A-2D show a series of graphs illustrating exemplary energy levels of data frames at full, half, quarter, and eighth rates.

Fig. 3 is a block diagram of a variable rate receiving system related to the rate setting characteristic of the present invention.

4 is a flow chart illustrating an exemplary embodiment of a processing step involved in a variable setting in accordance with performance by the processing element of FIG. 3.

5 is a block diagram illustrating elements of a variable rate receiving system in which a RAKE receiver is used.

Detailed description of the preferred embodiment

1 shows an exemplary cellular mobile telephone system in which the present invention is used. To illustrate this exemplary embodiment, a description will be given under the background of a CDMA cellular communication system. However, it is to be understood that the present invention is applicable to other forms of communication systems such as personal communication systems (PCS), wireless subscriber lines, branch exchange (PBX) or other known systems. Moreover, the invention may be used in other spread spectrum systems as well as in systems using other known transmission modulation schemes such as TDMA and FDMA.

In FIG. 1, the system controller and switch 10 typically include hardware interface and appropriate interface with hardware to provide system control information to the cell site. The controller 10 controls the routing of the telephone cell to the appropriate cell site from the public switched data network (PSTN) for transmission to the appropriate mobile unit. The controller 10 also controls the call routing of the PSTN from one mobile unit through one or more cell sites. The controller 10 typically enables direct calls between mobile users through appropriate cell site stations because such mobile units cannot communicate directly with other using units.

The controller 10 may be coupled to the cell site by radio frequency communication or by various means such as an optical fiber link or a dedicated telephone line. In FIG. 1, two example cell sites 12 and 14 are shown together with two example mobile units comprising a cellular telephone. Arrows 20a and 20b and 22a and 22b define possible communication links between cell site 12 and mobile units 16 and 18, respectively. Similarly, arrows 24a and 24b and arrows 26a and 26b define possible communication links between cell site 14 and mobile units 18 and 16, respectively. The cellular system shown in FIG. 1 may use a variable rate data channel for communication between cell sites 12 and 14 and mobile units 16 and 18. By way of example, a vocoder (not shown in the figure) is based on voice activity during 20 millisecond (ms) frames of data, with four different, such as about 8,550 bits per second (bps), 4,000 bps, 2,000 bps and 800 bps. Sample speech information may be encoded into symbols at a rate. As explained in the IS-95-A standard, each frame of vocoder data is formatted with overhead bits according to 9,600 bps, 4,800 bps, 2,400 bps and 1,200 bps data frames. As described above, the highest rate data frame corresponding to 9,600 bps is called full rate frame, the 4,800 bps data frame is called half rate frame, the 2,400 bps data frame is called quarter rate frame, and the 1,200 bps data frame is 1 / This is called an 8 rate frame. While these examples describe four data rates in one set, a different number of variable rates may be used instead. 2A to 2D show a form in which a variable rate data frame is added to a system using four rates as one set. As shown in Figs. 2A to 2D, the energy of the data frame varies as the data rate of the data signal varies. Moreover, when the data rate is lower than the maximum, in addition to lowering the energy, each data symbol of the frame is repeated as many times as required to achieve a certain number of symbols in each frame to be transmitted. In FIG. 2A, a data frame designated as a traffic packet is represented by symbols P ₁ to P ₁₆ . The data frame of FIG. 2A was encoded at full rate with the highest energy without symbol repetition. 2B shows a half rate data frame with half of the highest energy with each symbol P ₁ to P ₈ repeated twice. 2C shows a quarter data frame with one quarter of the highest energy with each symbol P ₁ to P ₄ repeated four times. 2D shows a 1/8 rate data frame with 1/8 of the highest energy with each symbol P ₁ to P ₂ repeated 8 times. Although the fractions of energy in FIGS. 2A-2D are equal to the fractions of the data symbols of the frame, it should be understood that different fractions of energy may be used instead.

In addition to encoding with data symbols, a data frame is typically formatted with overhead bits that include additional bits for error correction and detection, such as cyclic redundancy check (CRC) bits. The CRC bit can be used by the decoder to determine whether a frame of data has been correctly received. The CRC code is generated by dividing the data block by a predetermined binary polynomial as described in detail in IS-95-A. Other methods of detecting whether a frame was received correctly include Yamamoto quality metrics and symbol error rates. Yamamoto Metrics compares the difference of the threshold and the difference in the Mactrix, which remerged the path at each step of Viterbi decoding, and labels it as an unreliable path if the matrix difference is less than the quality threshold. Is set. If the final path selected by the Viterbi decoder is labeled as unreliable at any stage, the decoder output is labeled as unreliable. Others are labeled as trusted. The symbol error rate is set by taking the decoded bits, re-encoding these bits to provide a re-encoded symbol, and comparing these re-encoded symbols with difficult-to-set received symbols. The symbol error rate is a mismatch measure between the re-encoded symbol and the received symbol.

The formatted data frame further undergoes processing including amplification of the data frame signal and frequency upconversion to a radio frequency (RF) frequency band prior to transmission.

When a signal of a variable rate data frame is received by a mobile unit such as mobile unit 16 or 18 of FIG. 1, the mobile unit must set the transmission rate to decode the signal appropriately. However, the rate of received frames is not known by conventional mobile stations. Moreover, if it is impossible to set the rate by examining the absolute power of the received signal, the power is proportional to the transmission rate. This is due to changes in propagation paths such as fading and blocking. Transmitted signals are reflected from many different types of physical environments. As a result, the signal reaches the receiver of the mobile unit with multiple reflection components. In the UHF frequency bands commonly used for mobile wireless communications, including the frequency bands of cellular mobile telephone systems, sufficient phase difference occurs for signals traveling on different paths. Off-phase components may significantly reduce and reduce the received signal power. Fading is described in more detail in US Pat. Nos. 4,901,307 and 5,103,459. Blocking occurs because of physical obstacles entering the sight propagation path line.

Although it is impossible to set the encoded rate of the data frame by examining the absolute power of the received data signal, the rate can be set if the fading characteristic is known. The present invention performs rate setting by comparing the power of the reference signal and the power of the data signal transmitted from the same source. The signal transmitted at constant power should always be the reference. Moreover, because fading is frequency dependent, the reference signal should be transmitted at approximately the same frequency as the data signal. In this way, the data and the reference signal exhibit similar fading characteristics, and the rate of the data signal can be set according to the power of the data signal relative to the power of the reference signal.

In a preferred embodiment, the reference signal consists of the pilot signals disclosed in US Pat. Nos. 4,901,307 and 5,103,459 described above. It is known to use pilot signals in CDMA systems. As disclosed in the above patents, a pilot carrier signal is used to provide an interference phase reference for the communication link. In a CDMA cellular system, each cell or sector transmits a pilot signal with the same spreading code but different code phase offsets. Since the pilot signals are distinguished from each other by the phase offset, the cell sites or sectors are transmitted separately. The use of the same pilot signal code enables the mobile unit to search for a system that is time-synchronized by a single search of all pilot signal code phases. The pilot signal is also used as a reference time for demodulation of the digital voice signal transmitted by a particular cell site.

3, an exemplary receiving system for receiving variable rate communication is described. In a CDMA environment, for example, the receiving system of FIG. 3 may be implemented in a mobile unit to set the data rate of the signal transmitted from the cell site. The present invention provides a particular advantage for the mobile station because it can be avoided to decode all at all rates by setting the rate prior to decoding. This reduces power consumption with decoding processing that can extend the battery life of the receiver. In addition, the speed of rate setting is improved.

To explain FIG. 3, the mobile unit in which the rate setting system is implemented is called a mobile unit N, which is represented by either the mobile unit 16 or the mobile unit 18 of FIG. 1. It may be. Variable rate data is transmitted from the system controller and the switch 10 to the mobile unit N via one or more cell sites. This cell site is called a cell site N 'and is represented by either the cell site 12 or the cell site 14 of FIG. Although the rate setting system is shown in FIG. 3, this rate setting system is part of the mobile unit N, which may instead be implemented at the cell site to set the data rate of the signal transmitted from the mobile unit. It should be understood that. The rate setting system may also be used for other communication systems.

The variable rate receiving system shown in FIG. 3 includes a receiver 30 for correcting a cell site transmission signal. The signal received by receiver 30 comprises the RF signals of the pilot and data signals transmitted by cell site N '. Receiver 30 frequency downconverts the received signal from an amplified and RF frequency band to an intermediate frequency (IF) band.

The IF signal is sent to pilot demodulator 32 and traffic demodulator 34. The design and implementation of demodulators 32 and 34 are disclosed in US Pat. No. 5,490,165 entitled “DEMODULATION ELEMENT ASSIGNMENT IN A SYSTEM CAPABLE OF RECEIVING MULTIPLE SIGNALS”, assigned to the assignee of the present invention and referenced herein. Pilot demodulator 32 demodulates the IF signal to generate a pilot signal transmitted by cell site N ', and sends the pilot signal to pilot power measurement element 36. Traffic demodulator 34 demodulates the IF signal to generate a data or traffic signal consisting of a symbol of one frame of data transmitted by cell site N '. Traffic demodulator 34 produces a data signal by despreading and correlating the IF signal with a pilot signal identifying cell site N '. The data signal generated by the traffic demodulator 34 is transmitted to the traffic power specifying element 38. The data signal is also sent to the decoder 40.

In the example embodiment, decoder 40 is a trellis decoder capable of decoding variable rate data, such as a Viterbi decoder. The design and implementation of a multi-rate Viterbi decoder that decodes all received signals at all rates in one set of rates is described above. Patent applications 08 / 126,477 and 08 / 233,570 are disclosed. It will be understood by those skilled in the art that multiple Viterbi decoders may be modified to decode at a selected rate. This may be accomplished by having a Viterbi decoder that receives an input representing the rate in response to decoding the data signal in accordance with the rate indicated by the decoder.

Each of the pilot power measuring element 36 and the traffic power measuring element 38 measures the power of the demodulated pilot signal and the demodulated traffic signal. The signal of the power level is transmitted to the rate setting element 42.

For the purpose of explanation, the rate setting element 42 will be described for setting the data rate used using four possible rates as one set. It should be understood that the rate setting element 42 may be modified to accommodate different numbers of possible data rates. Another change may cause rate setting element 42 to first select a subset of the data rate from a set of all possible rates, and then set the correct data rate from the subset of data rates.

The rate setting element 42 consists of a memory 44 and a rate processor 46. Memory 46 stores a reference ratio of the power of the pilot signal transmitted by cell site N '(P _{full rate} / P _pilot ) and the power of the full rate frame transmitted by cell site N'. In addition, the memory 44 has a reference ratio of the power of the full rate frame and the half rate, the quarter rate, and the power of the 1/8 rate frame (P _{half rate} / P _pilot , P _quarterrate / P _pilot , P _{1/8 rate).} / P _pilot ) can also be saved. The latter three ratios indicate that the power of the transmitted half rate, quarter rate and 1/8 rate frames is not exactly 1/2, 1/4 and 1/8 of the power of the full rate frame, respectively.

In a preferred embodiment, upon establishment of a link between mobile unit N and cell site N ', cell site N' transmits an initial ratio of full-rate frame power to pilot power, which initial ratio is a memory as full-rate reference ratio. Stored at 44. In addition, cell site N 'transmits an initial ratio of half rate, quarter rate, and eighth rate frame power to pilot power, and these ratios are the memory (44) ratios as half rate, quarter rate, and eighth rate reference ratio, respectively. )

Rate processor 46 receives a signal indicative of the power level of the demodulated pilot signal and the demodulated data signal. For each frame of the received data signal or the traffic signal, a rate processor 46 calculates the ratio of the frame of the data signal for the power of the pilot signal (P _{bit paepik} / P _pilot) power. The rate processor 46 then compares the full rate reference ratio (P _{full rate} / P _pilot ) and the frame _rate (P _traffic / P _pilot ). Also, the half rate, quarter rate and 1/8 rate reference ratios are useful, and the frame ratios are compared with these. If the frame ratio is equal to the reference ratio, processor 46 receives a full rate frame of data and sends a signal indicative of the full rate to decoder 40. Similarly, when the frame ratio represents a half rate, quarter rate, or ratio of 1/8 rate frames, a signal indicative of the selected rate is provided to the decoder 40.

Instead of defining the reference ratio to be P _pooled / P _pilot , the reference ratio may be P _pilot / P _pooled . Here the reference ratio is P _pilot / P _{full rate} , and rate processor 46 calculates the frame ratio of the power of the pilot signal to the power of the data signal. The frame ratio can be compared again to the reference ratio to estimate the frame rate and then provided to decoder 40.

Decoder 40 receives a signal and a demodulated data frame indicating the estimated data rate of the frame provided by rate setting element 42. Decoder 40 performs decoding and error correction on the demodulated data frame. Demodulated data frames consisting of data symbols are decoded at a rate provided by the rate setting element 42 to generate information bits. In addition, error metrics are generated that include cyclic redundancy code bits, Yamamoto quality metrics, and symbol error rates. Error metrics indicate the quality of the frame of information bits.

If the error metrics indicate that the data symbol has been properly decoded into information bits, decoder 40 provides a signal of the information bits to variable rate vocoder 48. However, if the data symbol indicates that it has not been properly decoded with the information bits, decoder 40 decodes all the demodulated data to set the most appropriate data rate. Methods of decoding all at all rates are disclosed in US patent applications 08 / 233,570 and 08 / 126,477. Next, the signal of the information bits decoded according to the most appropriate data rate is provided to the variable rate vocoder 48. Upon receipt of the signal of the information bits, the variable rate vocoder 48 further performs processing on the information bits for interfacing with the user.

The steps included in the rate setting described in the above embodiment are briefly shown in FIG. FIG. 4 is a block diagram illustrating a flowchart showing some steps included in the processing described with reference to FIG. 3.

In an alternative embodiment, instead of having a rate processor 44 that generates only a signal indicative of one of the rates set by the rate setting element 42, the processor 44 is a possible rate in order of decreasing probability. Can be graded. This class is provided to the decoder 40. Decoder 40 then decodes the signal of the data symbol according to the highest class rate and generates error metrics for the decoded bits. If the error matrix indicates good decoding, then the information bits are provided to the vocoder 48. Otherwise, the signal of the data symbol is decoded sequentially at different rates according to the class, and error metrics are generated for each decoding. Once the error metrics indicate high quality, no further decoding is needed.

In another embodiment, rate setting system 42 is performed in conjunction with a different rate setting system to provide additional metrics based on the set rate of the received frame. For example, rate setting system 42 may be used in conjunction with the method of decoding both disclosed in US Patent Application Nos. 08 / 233,570 and 08 / 126,477. In particular, this is useful where very accurate rate settings are required.

The rate setting system described above assumes that the ratio of full-rate traffic channel power to pilot channel power remains constant during the communication link. However, in a CDMA system, the cell site may adjust the power of the transmitted signal in response to a power conditioning request from the mobile unit. Adjustments are made to maintain the quality of the communication link. In one embodiment of the CDMA system, the mobile unit may compare the power of the signal received from the particular cell site with the interference and noise power. With the signal-to-interference ratio deviating from the ideal value, the mobile unit may send a request for the cell site for adjustment of cell site transmit power. A detailed description of power control is disclosed in US Pat. No. 5,485,486 entitled “METHOD AND APPARATUS FOR CONTROLLING TRANSMISSION POWER IN A CDMA CELLULAR MOBILE TELEPHONE SYSTEM”, assigned to the assignee of the present invention and referenced herein.

When the cell site adjusts the power of the transmitted signal, the rate setting element 42 of FIG. 3 can be updated by adjusting the value of the reference ratio (P _{full rate} / P _pilot ) stored in the memory 44. This is the ratio of the power of the pilot signal to the power of the full rate traffic signal. In a system using additional reference ratios (P _halfrate / P _pilot , P _quarterrate / P _pilot , P ₁ / _8rate / P _pilot ), these ratios can also be adjusted. In an improved embodiment of the rate setting system of the present invention, the mobile unit tracks the power control request sent to the cell site. A signal indicative of the power control request is sent to the rate processor 46 of the rate setting element 42. Based on the power control request, the rate processor 46 estimates the updated reference ratio P _{full rate} / P _pilot and sends the updated value to the memory 44 for storage. Similarly, rate processor 46 may estimate the updated reference ratio P _{half rate} / P _pilot , P _quarterrate / P _pilot , P _{1/8 rate} / P _pilot . The sequential rate setting of the data frame is performed based on the updated reference ratio or ratio.

It should be understood that the receiving system shown in FIG. 3 does not need to set the rate of the received frame if the rate is set only once per frame. The system described above can measure the power of a received signal several times over a time frame. Traffic power measurement element 38 may be configured to accumulate power measurements from the beginning of the frame to the end of the frame. Thus, traffic power measurement 38 calculates a new average of power measurements every hour and new power measurements are made by traffic frames. Similarly, pilot power measurement element 36 may accumulate power measurements for pilot signals during a data frame period. At any moment during the frame, the P _traffic / P _pilot may be calculated to obtain an optimal estimate based on the portion of the data frame received up to that moment. The data rate for the _traffic frame may be set at any instant based on the P _traffic / P _pilot . This is very important for applications requiring fast rate setting. For example, a power control design that measures the strength of a data signal several times during a frame needs to know the actual frame rate for assessing the quality of the communication link. The drop in power of the data signal may depend on fading or low data rate. This needs to be set before the power control command is sent.

In a further improved embodiment of the rate setting system of the present invention, the cell site maintains tracking of the transmitted pilot signal power in relation to the full rate traffic signal power. The cell site then intermittently transmits a signal of an estimated non-P _{full rate} / P _pilot representing the relative power of the transmitted signal. The signal ratio is received by the mobile unit. With continued reference to FIG. 3, the rate processor 46 of the rate setting element 42 obtains the reference ratio and compares the value of the newly received ratio with the value of the reference signal received from the memory 44. If the reference ratio is different from the newly received ratio, the reference ratio is updated with the newly received ratio. The update reference ratio is then used to set the rate of the sequentially received data frame. In addition to P _{full rate} / P _pilot transmission, the cell site may intermittently transmit signals of estimated non-P _{half rate} / P _pilot , P _quarterrate / P _pilot , and P _{1/8 rate} / P _pilot . In this case, the additional ratios are compared with reference to the ratios stored in memory 44, and the reference ratios are updated if necessary.

In another embodiment of the present invention, a RAKE receiver is used in a receiving system for performing rate setting. The RAKE receiver demodulates multiple pilot and traffic signals as disclosed in US Pat. No. 5,109,390 entitled “DIVERSITY RECEIVER IN A CDMA CELLULAR TELEPHONE SYSTEM”, assigned to the assignee of the present invention and referenced herein. 5 illustrates the use of a RAKE receiver. In FIG. 5, receiver 30 receives cell-site transmit RF signals and frequency downconverts these signals to generate an IF signal. As shown in FIG. 3, instead of transmitting the IF signal to one pilot demodulator 32 and one traffic demodulator 34, the IF signal is a plurality of k shown as pilot demodulators 32a to 32c in FIG. And a plurality of k traffic demodulators, shown as pilot demodulators and traffic demodulators 34a to 34c in FIG.

The system of FIG. 5 may be implemented in a mobile unit. In the mobile unit, the k pilot demodulators 32a through 32c may demodulate multiple pilot signals that may correspond to or be transmitted from one or more cell sites from a given cell site. Similarly, k traffic demodulators 34a through 34c may demodulate traffic signals transmitted from one or more cell sites or from one given cell site. The k traffic demodulator is configured to receive multiple transmissions of the same source traffic signal, and the k pilot demodulator demodulates a pilot signal corresponding to multiple transmissions of the source traffic signal.

The demodulated pilot signal generated by the pilot demodulators 32a through 32c is transmitted to pilot power measurement elements 36a through 36c that measure the power of the demodulated pilot signal. The signal of the measured power of the pilot signal is sent to summer 50 which calculates the sum of the power of the pilot signal. Although a number of k pilot power measurement elements 36a through 36c have been shown, the signal pilot power measurement element can receive all demodulated pilot signals, measure the power of each signal, and sum the two powers. The summed signal is sent to a rate processor 46 which processes the signal as described above.

The demodulated traffic signal generated by the traffic demodulators 34a through 34c is transmitted to the corresponding traffic power measuring elements 38a through 38c that measure the power of the demodulated traffic signal. The signal of the measured power of the traffic signal is sent to summer 52 which calculates the sum of the power of the traffic signal. For pilot signals, a single traffic power measurement element can receive all demodulated traffic signals, measure the power of each traffic signal, and sum this power. The sum signal of the traffic signal power is also sent to the rate processor 46. Upon receiving the sum of the pilot signal powers and the sum of the traffic signal powers, the rate processor 46 sets the rate of the traffic signal as described above.

The foregoing description of the preferred embodiments enables those skilled in the art to make and practice the invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments that do not utilize the present invention. Thus, the present invention should not be limited to the embodiments shown herein but should be understood to be the broadest scope having the principles and novel features disclosed herein.

The present invention relates to digital communication. In particular, the present invention relates to a novel and improved system and method for setting a rate at which data is encoded for transmission at a receiver of a variable rate communication system.

Claims (25)

In a variable rate communication system, a subsystem for setting a data rate of a traffic signal received at a receiver includes: A traffic signal power measuring means for measuring the power of the traffic signal and providing a signal indicative of the measured traffic signal power; Pilot signal power measuring means for measuring the power of a pilot signal and providing a signal indicative of the measured pilot signal power; and A rate for receiving the traffic signal power and the pilot signal power, setting a data rate of the traffic signal according to the traffic signal power and the pilot signal power, and generating a signal indicative of the data rate selected for the traffic signal And a setting means. The method of claim 1, wherein the rate setting means, Memory means for storing a reference ratio of the power of a full rate traffic signal and the power of said pilot signal, and And a rate processor means for generating a frame ratio of said traffic signal power and said pilot signal power, comparing said reference ratio and said frame ratio to set a data rate of said traffic signal and generating said selected data rate. Rate setting system to do. 2. The rate setting system according to claim 1, further comprising decoding means for decoding the traffic signal based on the selected data rate to produce a decoded traffic signal. 4. The rate setting system according to claim 3, wherein the decoding means also generates an error matrix indicative of the decoded traffic signal quality. 5. The rate setting system of claim 4, wherein the decoding means further decodes the traffic signal based on one or more unselected transmission rates when a negative indicator of the energy matrix occurs. 2. The rate setting system of claim 1, further comprising CDMA receiver means for receiving the traffic signal and the pilot signal. The method of claim 2, The memory means also stores an additional reference ratio of the power of the traffic signal and the power of the pilot signal at a rate less than full rate, And said rate processor means further compares said additional reference ratio with said frame rate to set a data rate of said traffic signal and generate said selected data rate. 3. The rate setting system according to claim 2, wherein said rate processor means also tracks a power control request sent from said receiver to a transmitter and adjusts said reference ratio stored in said memory means in response to said power control request. . 3. The apparatus of claim 2, further comprising receiver means for intermittently receiving a signal indicative of an updated ratio of power of the traffic signal transmitted at full rate to power of the pilot signal, And said rate processor means also replaces said update ratio and said reference ratio stored in said memory means. 9. The apparatus of claim 8, further comprising receiver means for intermittently receiving a signal indicative of an updated ratio of power of the traffic signal transmitted at full rate to power of the pilot signal, And said rate processor means also replaces said reference ratio stored in said memory means with said update ratio. The method of claim 1, The traffic signal power measuring means measures the power of the traffic signal several times during a received data frame, obtains an average of the power of the traffic signal each time the power of the traffic signal is measured, The pilot signal power measuring means measures the power of the pilot signal several times during the received data frame, obtains an average of the power of the pilot signal each time the power of the pilot signal is measured, And the rate setting means sets a data rate of the traffic signal in accordance with an average of power of the traffic signal and an average of power of the pilot signal. A receiver receiving a wideband signal, A demodulator that demodulates the wideband signal to produce a traffic signal and a pilot signal, wherein the traffic signal is transmitted at one of a possible set of transmission rates, and the pilot signal is transmitted at a constant power and has a carrier frequency equal to the traffic signal Demodulator, Power measurement means for measuring the power of the traffic signal and the power of the pilot signal; Rate setting means for setting a data rate of the traffic signal in accordance with the traffic signal power and the pilot signal power to generate a signal representing a data rate selected for the traffic signal; Receiving means for decoding said traffic signal in accordance with said selected data rate. The method of claim 12, wherein the rate setting means, Memory means for storing a reference ratio of power of a full rate traffic signal and power of said pilot signal, And a rate processor means for generating a frame ratio of power of said traffic signal and power of said pilot signal, comparing said reference ratio and said frame ratio to set a data rate of said traffic signal and generating said selected data rate. Receiving system characterized by. 13. The receiving system of claim 12, wherein the demodulator is a CDMA demodulator. A receiver in a variable rate communication system, the method of setting a data rate of a received traffic signal, comprising: A traffic signal power measurement step of measuring a power of the traffic signal and providing a signal representing the measured traffic signal power; A pilot signal power measurement step of measuring a power of a pilot signal to provide a signal indicative of the measured pilot signal power, and Setting a data rate of the traffic signal in accordance with the traffic signal power and the pilot signal power to provide a signal indicative of a selected data rate. The method of claim 15, wherein setting the data rate comprises: Storing a reference ratio of the power of the full rate traffic signal and the power of the pilot signal in a memory, Generating a frame ratio of said traffic signal power and said pilot signal power; and And comparing the reference ratio and the frame ratio to set the data rate for the traffic signal. 16. The method of claim 15, further comprising a traffic signal decoding step of decoding the traffic signal based on the selected data rate to produce a decoded traffic signal. 18. The method of claim 17, further comprising generating an error matrix indicative of the quality of the decoded traffic signal. 19. The method of claim 18, further comprising decoding the traffic signal based on one or more unselected data rates upon generation of a negative indicator of the error metric. 17. The method of claim 16, further comprising: storing in the memory an additional reference ratio of power of the traffic signal at a rate less than full rate and power of the pilot signal, and And comparing the additional reference ratio and the frame rate to set the data rate for the traffic signal. 17. The method of claim 16, further comprising: tracking a power control request sent from the receiver to a transmitter, and And adjusting the reference ratio stored in the memory in response to the power control request. 17. The method of claim 16, further comprising: intermittently receiving a signal indicative of an updated reference ratio of power of the pilot signal and power of the traffic signal transmitted at full rate; If the reference ratio is different from the updated ratio, replacing the reference ratio stored in the memory with the updated ratio. 22. The method of claim 21, further comprising: intermittently receiving a signal indicative of an updated reference ratio of the power of the traffic signal transmitted at full rate relative to the power of the pilot signal; If the reference ratio is different from the updated ratio, replacing the reference ratio stored in the memory with the updated ratio. The method of claim 15, Setting the data rate of the traffic signal comprises: Measuring the power of the traffic signal and the power of the pilot signal several times during a received data frame, Each time measuring the power of the traffic signal and the power of the pilot signal during the received data frame, calculating an average of the power of the traffic signal and the power of the pilot signal; and And setting the data rate according to the average of the power of the traffic signal and the average of the power of the pilot signal. In a variable rate communication system, an apparatus for setting a data rate of a traffic signal received at a receiver includes: Pilot signal power meter with input and output, A traffic signal power meter having an input and an output, and And a rate processor having a first input coupled to the pilot signal power meter output, a second input coupled to the traffic signal power measurement output, and an output providing a rate for the traffic signal. Setting device.